Optical systems exposed to harsh environmental conditions typically include a transparent window of a suitable durability to protect the delicate optical elements of the system (e.g., mirrors or lenses) from the environmental conditions. Exposure to environmental conditions can result in misalignments of the optical elements, among various other undesirable effects on system performance. While providing protection for the more delicate optical elements of an optical system, the availability of materials for an optical window transparent to a wide spectral range is very limited. Consequently, typical broadband optical system designs require a compromise between spectral coverage and system performance.